Devices of this type are used, for example, in paper-processing machines, such as enveloping machines, printers or copiers, for example. The products to be rotated can be, for example, individual sheets or sheets of paper, or a stack of sheets consisting of at least two sheets. However, devices of this type can also be used for rotating other flat products, such as, for example, for rotating plastic films, cardboard sheets or the like, or also for rotating bound or stapled sheets in the form of catalogs, brochures, notebooks or similar products.
From U.S. Pat. No. 3,758,104, a device for rotating rectangular cardboard sheets by 90° is known, wherein the sheets are deposited in a predetermined orientation for further processing in a container. This known device comprises a conveyor belt that is moved at a first speed in a transport direction, in order to move the cardboard sheets to be rotated by an angle of 90° in a first orientation toward a rotating device. The rotating device has a first slit and a second slit, wherein a first section of the cardboard sheet to be rotated is engaged in the first slit, and a second section of the cardboard sheet is engaged in the second slit. The first slit here comprises a first pressure roller, which defines a slit between its outer periphery and the conveyor belt, in which the first section of the cardboard sheet is engaged. The second slit is defined by a rotating roller pair with a driven rotating roller and a pressure roller, between the outer periphery of which the second section of the cardboard sheet to be rotated engages. The driven roller of the rotating roller pair is driven in order to rotate the cardboard sheet at a speed that is different from the transport speed of the transport track.
EP 0 814 041 B1 discloses a method for rotating sheets from a first orientation into an orientation that is perpendicular to the former orientation as well as a sheet stacking device, in which sheets to be stacked according to the method are rotated from a first orientation into an orientation that is perpendicular to the former orientation. The sheets to be rotated are moved evenly during the rotating between a position located upstream and a position located downstream, and are moved differentially in an intermediate movement phase without any change in the speed component in the advance direction of the sheet. In the intermediate movement phase (rotating phase), the sheet is moved with a speed-time profile that includes a first speed function at which the movement speed is increased temporarily by a certain amount, and a second speed function at which the movement speed is decreased temporarily by the same predetermined amount, and at the same time, in order to rotate the sheet by an angle of rotation, wherein the amount of the rotation angle is determined by the duration of the increased or reduced movement speed. Simultaneously with the rotation of the sheet, a lateral shift occurs, which is determined by the fact that the time at which the rotation of the sheet is started is selected appropriately, with regard to the arrival of the sheet at a fixed reference point. The rotation of the sheet here occurs by means of a rotating device, which comprises, transversely to the advance direction of the sheet, mutually spaced roller pairs, which are driven by a step motor, in order to produce the predetermined speed-time profiles of the roller pairs.
These devices and methods known from the prior art for rotating flat products, such as, sheets, stacks of sheets, or paper sheets, can be used only at relatively low transport speeds of the product to be rotated owing to the accelerations and decelerations that occur during the rotating process. In modern paper-processing machines with high throughput numbers on the order of 100,000 products per hour, the products to be rotated have to be strongly decelerated and accelerated again during the rotating process if the rotating process by a certain rotation angle, 90°, for example, is carried out in a single rotating step. To prevent strong decelerations and accelerations of the product, it is already known in the prior art to divide the entire rotating process into two or more partial steps.
Dividing the entire rotating process into two or more partial steps makes it possible, at a very high cycle output or decreasing cycle time, for more time and more space to be available for the individual rotating processes. The cycle output can be increased in the case of a division of the entire rotating process into two or more partial steps, because the subsequent product can already be introduced into the first rotation device while the preceding product is still in the rotating process in a downstream rotating device.
Thus, for example, DE 3718206 A1 discloses a transport device for rotating stacks of sheets moved along a turning section, which comprises a turning conveyor consisting of conveyor belts that extend next to one another in two tracks and are driven at different speeds, wherein a first track comprises a circulating conveyor belt that can be driven at a first speed, and the second track comprises at least two circulating conveyors one after the other in the transport direction, which are driven at a speed different from the first speed. Due to the different speeds of the first track and the several conveyors of the second track, a rotation by a certain predetermined rotation angle occurs of the stack of sheets resting on the two tracks, which angle depends on the difference in the speeds of the first track and of the second track. Here the conveyor belts of the first track and of the second track are provided in each case with bristles on their upper side that supports the stack of sheets, in order to ensure a satisfactory adhesion between the upper side of the conveyor belts and the bottom side of the stack of sheets. The adhesion of the stack of sheets to the conveyor belt is here permanent. This can lead to problems during the transfer of a stack of sheets from a conveyor of the second track to a subsequent conveyor of the second track, since the stack of sheets, at least for a short time, is engaged simultaneously in two conveyors, which each exert a possibly different torque on the stack of sheets. This can lead to buckling or stretching of the sheet or to a slipping of the stack of sheets.
US2009/0107892A1 discloses a device for rotating mail items, which are moved along a transport track, from a first orientation into a second orientation. The device comprises several roller pairs arranged one after the other in the transport direction, which are arranged with a mutual spacing in the transverse direction relative to the transport direction. The roller pairs, which are arranged at a transverse separation from one another, are driven, for the purpose of rotating the mail items, at different speeds, wherein a rotation by a predetermined rotation angle, which depends on the speed difference of the roller pairs that can be different for each roller pair, is imparted to the mail item in each of the roller pairs. The arrangement of the roller pairs comprises, at the beginning and the end, in each case one roller pair by means of which the mail item is not rotated but is continued to be moved linearly in the transport direction. During the rotating of a mail item by the roller pairs arranged at a mutual transverse separation from one another, the mail item is moved on in the transport direction. The lateral separation of corresponding rollers of a roller pair can here be set so as to produce a defined rotation of the mail item in the roller pair in question, and to set a displacement of the mail item.
The known rotating devices and methods, in which the entire rotating process is carried out in at least two partial steps, are, however, found to be disadvantageous, since the separation of the pivot points in the lateral direction (transport direction) is fixed and cannot be adapted. This is particularly disadvantageous if the same rotating device is to be used to process products, for example, sheets, having different formats. Moreover, in the case of the known rotating devices and methods, in which the entire rotating process is carried out in partial steps in several rotating devices arranged one after the other, there is a risk that, at the time of the transfer of the product from one rotating direction into the subsequent rotating direction, buckling or stretching of the product occurs, which can damage the product or lead to failures of the rotating devices. In the known rotating devices, the rotating devices located one after the other in the transport direction are arranged at a fixed and short mutual separation. When processing products with larger dimensions, in particular, this leads to the possibility that a product can be engaged simultaneously in two adjacent rotating devices, which can lead to the product being stretched, buckled or bent, and damaged as a result.